We propose to investigate several aspects of the structure and replication of enveloped RNA viruses. We have been studying defective-interfering (DI) particles of Sindbis virus and plan to continue the characterization of the defective RNA. We shall examine the role of DI particles in establishing and maintaining persistent infections in cultured cells. A major objective in this proposal is to determine the role of carbohydrates on the structure and replication of Sindbis virus and vesicular stomatitis virus (VSV). In these studies we are using the antibiotic tunicamycin to inhibit glycosylation completely and cell variants in which the structure of the oligosaccharide chains is altered. We are examining what effect the absence of carbohydrate or different amounts of carbohydrate have on the structure and stability of the G protein.